This invention relates to a method for producing thin films having uniform molecular orientation. More particularly, this invention relates to a method for producing such films having a sufficient thickness to permit analysis of their structure by a variety of physical methods.
In order to adequately determine the structure of high molecular weight components of a biological membrane, it is often desirable that the membrane be incorporated into a relatively thick film on the order of at least about 5 microns in thickness and that the high molecular weight components be uniformly oriented. The higher the degrees of orientation, the more structural information can be obtained. Ideally this orientation is three-dimensional such as found in a crystal but can also be two-dimensional or one-dimensional such as found in various types of liquid crystals. In addition, the film must be deposited on a suitable substrate. Films having such a structure then can be analyzed advantageously by presently available techniques including X-ray scattering, visible-UV linear dichroism, polarized infrared absorption, polarized Raman light scattering, Fourier transform infrared spectroscopy, circular dichroism, nuclear magnetic resonance or polarized flourescence spectroscopy. By permitting the use of these and other analyzing techniques, it is possible to provide a precise picture of the structure of the molecular fragments forming the film. Such information would be useful for understanding the functioning of biological membranes from normal and diseased cells. Such information, also, would be useful in the design of films from other molecules such as liquid crystal forming compounds, polymer fragments or from molecular structures such as micelles, vesicles or artificial biological membranes in order to tailor the physical characteristics of the film as desired. For example, it would be desirable to provide thin films having photoconductive characteristics, the ability to selectively transport ions or other substances, light sensitivity or other energy transducing characteristics. It would also be desirable to provide thin films having uniform molecular orientation in order to produce a film which has a specific property, such as increased strength due to orientation or properties which can be utilized in precise analytical techniques. For example, it would be desirable to provide a permeable film having a surface or bulk volume which has a uniform concentration of a specific binding composition such as an enzyme, an antigen or an antibody so that the corresponding substrate, antibody or antigen thereby could be selectively isolated. Examples of other properties of films in which it would be desirable to provide specialized surface or bulk properties include photo-induced reactive films, multilayered films, each layer differing in composition and binding properties, or porous films containing oriented pores, or films with high tensile strength.
Prior to the present invention, a number of techniques have been available to form thin films having essentially uniform molecular orientation. Unfortunately, the films produced in the prior art techniques are too thin to afford their use in a wide variety of testing procedures and/or are not sufficiently molecularly oriented and/or cannot be deposited on the proper substrate. For example, one such technique utilizes a magnetic or electric field to orient the molecules forming the film. Another procedure utilizes hydrodynamic flow wherein the molecules comprising the film are oriented under the influence of a moving liquid stream. Alternatively, it has been proposed to dip a flat substrate repeatedly into an aqueous suspension containing the molecules used to form the film, wherein, after dipping, the aqueous solvent is evaporated prior to re-immersing the substrate into the solution. While all of these procedures yield films having their molecules oriented, the resulting film is too thin or the degree of molecular orientation is insufficient to permit accurate analysis of the molecules forming the film. It has also been proposed to form a film by centrifugation, e.g. J. Mol. Biol. (1975), 93, 123-138, Henderson. In this procedure, a film is spun down from a suspension of the film onto a flat surface within a centrifuge tube in order to form a film oriented well enough to carry out x-ray scattering experiments. While the surface of the film produced is oriented, the thickness of the film is not at all uniform. Furthermore, the orientation is dependent upon the density difference between the film fragments and the solution which can be very small. This phenomenon limits the orientation that can be obtained with this technique.
It would be highly desirable to provide a method and apparatus for forming thin films having uniform molecular orientation of sufficient and uniform thickness to permit their analysis by presently available techniques including x-ray scattering, polarized infrared absorption, UV-visible linear dichroism, or polarized Raman light scattering. Furthermore, it would be desirable to provide such films having uniform surfaces, compositions and properties such as optical properties, specific reactivity, electro-conductivity or electro-chemical properties.